The present invention relates to an epoxy microcapsule, an interfacial polymerization process of making the microcapsule, and the use of the microcapsule in a carbonless copying system. More particularly, the present invention relates to microcapsules having walls of low permeability and substantially no free unencapsulated oil that can be effectively used in a carbonless copying system to provide high quality images.
In a carbonless copying system, a plurality of substrates, e.g., paper sheets, are arranged in a manifold with each sheet having one or more coatings on its surface. The manifold is designed so that when external pressure, such as that caused by a typewriter, pen or other instrument, is applied to the outermost sheet, a colored image is formed on at least one surface of each sheet of the manifold.
Typically, microcapsules are used in such a carbonless copying system. For example, a coating of microcapsules is applied to the back surface of the top sheet of the manifold. The microcapsule contains an initially colorless chemically reactive color-forming dye precursor as the core or fill material. The front surface of the next sheet, which lies adjacent to the back surface of the top sheet, is coated with a material containing component, such as a phenolic resin or reactive clay, that is capable of reacting with the colorless dye precursor contained in the microcapsules to produce a color.
Thus, an external pressure on the front surface of the top sheet will rupture the microcapsules on the back surface and release the colorless dye precursor which then chemically reacts with the reactive component of the coated front of the adjacent sheet to produce a colored image corresponding to the area of pressure. Similarly, colored images are produced on each successive sheet of the manifold by the external pressure rupturing the microcapsules carried on the bottom surface of each sheet.
The quality of the colored images in the carbonless copying system depends, in part, on the quality of the microcapsules used to coat the surfaces of the sheets in the manifold. If the microcapsules have walls of relatively high permeability, the core material within the microcapsules passes through the microcapsule walls prior to the application of external pressure to rupture the microcapsules. This premature passage of the core material through the permeable microcapsule walls causes undesirable markings and discoloration to appear on the sheets of the manifold and results in insufficient core material being present within the microcapsule wall when pressure is applied to rupture the microcapsules.
Likewise, to enhance the resulting images in the carbonless copying system, it is desirable that, during the manufacture of the microcapsules, the amount of unencapsulated core material is minimized. Core material that is not encapsulated during the process of making the microcapsules is often wasted and will cause undesirable sheet discoloration on manifold, particularly Coated Front and Back (CFB) manifolds and self-contained products.
Thus, there is a need for microcapsules and a process of making microcapsules that are of relatively low permeability and which substantially lack free unencapsulated oil. There is also a need for a carbonless copying system that uses microcapsules having these properties.